The present invention relates to a water soluble azo dye composition containing a Bunte salt group and a method for making the azo dye composition.
Bunte salts are generally understood to be alkali-S-alkyl or alkali-S-aryl thiosulfates. As used herein, the concept of a Bunte salt group includes the alkali or ammonium salts of the xe2x80x94S2O3xe2x88x92 group which is linked to a carbon atom. Bunte salt dyes are generally disclosed in xe2x80x9cThe Chemistry of Synthetic Dyesxe2x80x9d, by Venkataraman, Volume 7, at pages 35 to 68, published in 1968, and hereby incorporated by reference. On page 60, it is specifically stated that when dyeing human hair with a Bunte salt dye, the hair must be first treated with a reducing agent. Bunte salts are hydrolyzed by aqueous acids with the formation of thiols. In alkaline medium they form the corresponding disulfides as well as other products. This reactivity is utilized for fixing dyes with Bunte salt groups on textile materials. The functional groups of the fibers, such as, the OH group of the cellulosics, the amino and thiol groups of wool, or the acid amide groups of synthetic polyamides, act in this reaction as nucleophilic agents. After pretreatment of cellulose with sodium sulfide solution or during the treatment of wool, polycondensation takes place on the substrate with the formation of disulfide bridges. A corresponding dyeing with Bunte salt dyes is therefore washfast. Processes for synthesizing compounds with Bunte salt groups, the properties of these compounds and their use are described in an article by H. Distler, entitled xe2x80x9cThe Chemistry of Bunte Saltsxe2x80x9d, published in Angewandte Chemie International Edition, Volume 6 (1967), No. 6, pages 544-553.
Hair dye compositions use either oxidative dyes or direct dyes. The oxidative dyes lead to shades with better covering power and better staying power, but they have the disadvantage of not being entirely harmless and of requiring an oxidation reaction which is generally accompanied by appreciable degradation of the keratin fibers. In addition, their staying power and their affinity for the hair usually results in the appearance of bands of demarcation between dyed ends and half-lengths and undyed roots.
These problems do not arise in the case of direct dyes. Using of direct dyes has the further advantage over oxidative dye precursors by potentially reducing risks of allergy. Among the direct dyes most commonly used are nitrobenzene derivatives. However, these nitrobenzene dyes do not sufficiently withstand repeated washing. To overcome this flaw, attempts have been made to replace nitrobenzene dyes with aminoanthraquinone dyes or azo dyes.
U.S. Pat. No. 3,334,085 discloses a disazo dyestuff corresponding to the formula:
Xxe2x80x94Nxe2x95x90xe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90xe2x95x90Nxe2x80x94X
wherein X is a radical of the benzene series bearing a pendant thiosulfate group in a position selected from the group consisting of meta and para with respect to the adjacent azo group, and R is the radical of a naphthol bearing at least one hydroxy substituent in the ortho position to the azo group. The dyestuff is further characterized in that at least one of the radicals of the benzene series positioned ortho to the hydroxy substituent bears in ortho position to the adjoining azo group, a group capable of forming a metal complex of chromium, cobalt, copper, nickel, or iron. The dyestuffs are suitable for coloring fabrics.
U.S. Pat. No. 3,415,606 discloses a method of dyeing human hair which includes treating the hair first in a mordanting step which comprises contacting the hair with a mercaptan which is adapted to form with the keratin of the hair one or more SH groups on the surface of the hair. Subsequently, the treated hair surface is reacted with an azo dye having a Bunte salt group wherein the Bunte salt group is positioned meta to the adjoining azo group and separated from the benzene radical by at least one alkyl group.
U.S. Pat. No. 3,496,207 discloses a method of preparing sulfonaphthylamino thiosulfates for use as dye intermediates for use in making water soluble monoazo dyes for cotton and cellulose fabric.
British Patent No 953,428 discloses water soluble azo-dyestuffs containing one or more thiosulfuric acid groups and processes for their manufacture.
One object of the invention is to provide a novel class of compounds for use in coloring fibers including natural and synthetic fibers such as cotton, nylon, wool, and the like.
Another object of the invention is to provide a class of Bunte salt azo dye compounds for use in coloring animal hair, which can be used in animal hair color systems which are substantially free of reducing or mordanting agents.
The invention comprises a compound of the formula 
wherein R1 and R2 are either hydrogen or a phenylamino radical such that R1 and R2 are different. The phenylamino radical can comprise phenylamine or a substituted phenylamine having a substituent selected from the group consisting of alkoxy, sulfonate, and thiosulfate. The alkoxy substituent can comprise a methoxy or an ethoxy substituent. The above Bunte salt azo dye composition was discovered to dye animal hair a strong color when applied to animal hair at ambient temperature. Surprisingly, it was discovered that it was not necessary to pre-treat the animal hair with a mordanting or reducing step prior to or simultaneously with the application of the dye. The elimination of the reducing or mordanting step in dyeing animal hair provides significant economic advantages, simplifies the dyeing process, and minimizes damage to the animal hair such as wool and yak hair. The compounds of the present invention were also successfully employed to color fibers such as cotton, nylon and the like.
The invention comprises a Bunte salt azo dye compound capable of causing coloration of fibers such as textile fibers and animal fibers such as wool, leather, and animal hair (excluding human hair), and a dye composition containing the Bunte salt azo dye compound. Although Bunte salt dyes have been employed in dyeing fibers, the use of such dyes, particularly for dyeing animal hair has required the pretreatment of the material to be dyed in order for the dye to perform effectively. Examples of combining such reducing or mordanting steps with application of Bunte salt dyes to fibers can be found in U.S. Pat. No. 5,071,641. Unlike the prior art Bunte salt azo type dyes which are generally employed to dye fibers such as animal hair, the Bunte salt group of the present invention is in a para position relative to the azo bond, attached directly to a connecting benzene ring of a phenylamino radical without an intervening carbon or oxygen atom. It is believed that the proximity of the para-Bunte salt group to the azo bond is a critical factor in eliminating the requirement for the mordanting or reducing step. In addition, such conventional Bunte salt azo dyes generally have at least one carbon atom between the Bunte salt group and the benzene ring adjoining the azo bond.
The Bunte salt azo dyes of the present invention are prepared by diazotization of the S-(4-amino phenyl) thiosulfate by reacting the primary aromatic amine with sodium nitrite in the presence of a mineral acid such as hydrochloric acid to form a diazonium salt, followed by a coupling of the diazonium salt under alkaline conditions (at a pH from about 8 to about 10) with a salt of an aryl amino hydroxy naphthalene sulfonic acid, such as phenyl J-acid or phenyl Gamma-acid. Phenyl J-acid is a term of the dye art referring to a compound having the molecular formula C16H13NO4S such as 2-phenylamino-5-naphthol-7-sulfonic acid, or 6-phenylamino-1-naphtol-3-sulfonic acid. Phenyl Gamma-acid is a term of the dye art referring to a compound having the molecular formula C16H13NO4S such as 2-phenylaminonaphthalene-8-hydroxy-6-sulfonic acid. The critical aspect of the process of the present invention is to provide a Bunte salt azo dye which includes an azo group having at least one Bunte salt group in a para position on a benzene ring relative to the azo group attached to that benzene ring. The use of the sodium S-(4-amino-phenyl)-thiosulfate as the starting material results in the Bunte salt group being para to the azo bond in the molecule.
The invention further comprises a method for coloring keratin fiber such as animal hair including wool and other animal fur comprising directly applying an aqueous based hair dye composition comprising a Bunte salt azo dye compound, without a reducing agent, to animal hair for a period of time sufficient to cause coloration of the animal hair. It was surprisingly discovered that a reducing agent was not required to assist the dye in bonding to the animal hair. The composition is applied to the animal hair and allowed to remain on the hair for about 5 to 50 minutes, depending on the type and texture of the animal hair. The animal hair is then rinsed well with water to remove the composition. The compositions of the present invention are very gentle to the animal hair because they do not require the use of reducing agents to pre-treat the animal hair before the dye is applied. This application method is similar to that described in U.S. Pat. No. 3,415,606 (Example 1), but without the mordanting pretreatment with thioglycolic acid solution. It was noted in U.S. Pat. No. 3,415,606 that hair which had not been subjected to the mordanting pretreatment only dyed very slightly in this manner.